The present invention relates in general to contact lithography techniques and, more particularly, to contact lithography systems and methods that utilize deformable masks for patterning non-planar surfaces.
In conventional contact photolithography, a substrate having a flat or flattened surface is coated with a photoresist material. A flat glass mask is then aligned over the photoresist material and is brought into intimate contact with the substrate. The flat mask includes a mask pattern defined by areas of the mask that are opaque to light emitted by an ultra violet (UV) lamp or other suitable exposure source, and areas of the mask that are transparent to light from the UV lamp. An exposure operation is then performed whereby the photoresist material on the substrate is selectively exposed to light from the UV lamp through the flat glass mask. In particular, the light emitted by the UV lamp transmits through the transparent portions of the mask and penetrates the photoresist material below. The photoresist material is photosensitive to the light, thereby altering the chemical resistance of those exposed regions of the photoresist material to a corresponding developer. The changed resistance regions of the photoresist material are referred to herein as the exposed regions. The areas of the mask that are opaque block the light from the UV lamp from altering those regions of the photoresist material corresponding to the opaque areas of the mask, thus defining unexposed regions of photoresist material.
A subsequent developing process is then performed, whereby the developer is used to remove either the exposed regions or the unexposed regions of photoresist material from the substrate, resulting in a pattern in the remaining photoresist material corresponding to the pattern on the mask. In this regard, the corresponding pattern may be a positive or negative image of the mask pattern, depending upon whether the developing process removes the exposed or unexposed regions of the photoresist material. Once the pattern is prepared in the photoresist material, any number of conventional processes may be carried out. For example, subsequent deposition or etching processes may be performed as the specific application requires.
Photosensitive compounds are capable of producing patterns having a relatively fine feature size. However, as the desired feature size gets smaller, it becomes increasingly important for intimate contact to be made between the photomask and the substrate. For example, at the edges of the pattern, light is scattered and diffracted. Accordingly, if sufficiently intimate contact between the photomask and the photoresist material is not achieved, then it is possible for regions of the photoresist that are intended to be unexposed, e.g., regions of the photoresist that are proximate to the opaque edges of the pattern, to unintentionally become exposed, thus resulting in an inaccurate transfer of the pattern from the mask to the substrate.
There are an increasing number of applications where it is desirable to pattern non-planar surfaces. For example, many frequency selective surfaces such as those found on radomes, windows, the receiving surfaces of RF antennas, etc., are non-planar surfaces that may require a micromesh or other suitable pattern applied thereto. However, any curvature in the surface complicates the patterning process and makes the achievement of precise patterns difficult. Moreover, a flat glass mask may not be capable of projecting a useful image onto a non-planar substrate. For example, as the resolution and size of the lines in the pattern are reduced, it may become extremely difficult to use a flat mask due to the distortion introduced from a lack of intimate contact between the mask and the non-planar portion of the corresponding substrate that is to be patterned.